Primordial Black Holes

García-Bellido, J.

doi:10.1007/978-981-15-4702-7_27-1

Cited by 2 publications

(4 citation statements)

References 85 publications

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“…The value of the quantum of entropy for black hole horizons remains a matter of debate. This value has been argued to be k ln 2, as was concluded in 1975 by DeWitt [103], then by Mukhanov [119], and by García-Bellido [120]. As mentioned, DeWitt also argued that k ln 2 is the maximum entropy that an elementary particle can carry, because the least information one can have about it is whether it exists or not, which is 1 bit.…”

Section: Black Hole Horizonsmentioning

confidence: 85%

Testing the Minimum System Entropy and the Quantum of Entropy

Hohm,

Schiller

2023

Entropy

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Experimental and theoretical results about entropy limits for macroscopic and single-particle systems are reviewed. All experiments confirm the minimum system entropy S⩾kln2. We clarify in which cases it is possible to speak about a minimum system entropykln2 and in which cases about a quantum of entropy. Conceptual tensions with the third law of thermodynamics, with the additivity of entropy, with statistical calculations, and with entropy production are resolved. Black hole entropy is surveyed. Claims for smaller system entropy values are shown to contradict the requirement of observability, which, as possibly argued for the first time here, also implies the minimum system entropy kln2. The uncertainty relations involving the Boltzmann constant and the possibility of deriving thermodynamics from the existence of minimum system entropy enable one to speak about a general principle that is valid across nature.

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Section: Black Hole Horizonsmentioning

confidence: 85%

Testing the Minimum System Entropy and the Quantum of Entropy

Hohm,

Schiller

2023

Entropy

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“…For all non-primordial black holes, which are all of stellar mass or larger, T H,r→∞ is extremely low compared to the current temperature T CBR = 2.725 K [50] of the cosmic background radiation [50]. For sufficiently small primordial black holes [51][52][53][54][55][56][57][58][59][60][61] (M < hc 3 8πGkT CBR = 4.50 × 10 22 kg ⇐⇒ r S < hc 4πkT CBR = 6.69 × 10 −5 m), T H,r→∞ > T CBR = 2.725 K obtains. But as of this writing, to the best knowledge of the author, no such sufficiently small primordial black holes-indeed, no primordial black holes at all-have been discovered [51][52][53][54][55][56][57][58][59][60][61].…”

Section: Review Of Basic Concepts Pertaining To Schwarzschild Black H...mentioning

confidence: 91%

“…For sufficiently small primordial black holes [51][52][53][54][55][56][57][58][59][60][61] (M < hc 3 8πGkT CBR = 4.50 × 10 22 kg ⇐⇒ r S < hc 4πkT CBR = 6.69 × 10 −5 m), T H,r→∞ > T CBR = 2.725 K obtains. But as of this writing, to the best knowledge of the author, no such sufficiently small primordial black holes-indeed, no primordial black holes at all-have been discovered [51][52][53][54][55][56][57][58][59][60][61]. Moreover, while there are rationales according to which primordial black holes might contribute, perhaps significantly, to cold dark matter, there also are both theoretical and observational upper limits on their abundance [51][52][53][54][55][56][57][58][59][60][61] and therefore also on their actual contribution to cold dark matter [51][52][53][54][55][56][57][58][59][60][61].…”

Section: Review Of Basic Concepts Pertaining To Schwarzschild Black H...mentioning

confidence: 99%

“…Moreover, while there are rationales according to which primordial black holes might contribute, perhaps significantly, to cold dark matter, there also are both theoretical and observational upper limits on their abundance [51][52][53][54][55][56][57][58][59][60][61] and therefore also on their actual contribution to cold dark matter [51][52][53][54][55][56][57][58][59][60][61]. Hence, while it is possible that they could contribute, perhaps significantly, to cold dark matter, as of this writing, to the best knowledge of the author, it is uncertain whether or not they actually exist [51][52][53][54][55][56][57][58][59][60][61].…”

Section: Review Of Basic Concepts Pertaining To Schwarzschild Black H...mentioning

confidence: 99%

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Firewalls, Hawking (Tolman) Radiation, and a Tentative Resolution of the Firewall-Mass Problem

Denur

2024

Preprint

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It has been theorized that black holes are surrounded by firewalls, although there is not universal agreement concerning this. We first review basic concepts pertaining to Schwarzschild black holes and Hawking radiation. Then we discuss the anticipation of Hawking radiation initially by R. C. Tolman and shortly thereafter with P. Ehrenfest, albeit for non-black holes. We compare evaporation into a vacuum at absolute zero (0 K) of black holes with that of non-black holes, and show that not only black holes but also non-black holes evaporate in finite time. Next, we show that (i) if firewalls exist, they can originate via Hawking radiation at the minimum possible ruler distance (the Planck length) beyond the Schwarzschild horizon, where it has not suffered any gravitational redshift, or, alternatively, suffered maximal gravitational blueshift and (ii) the firewall temperature is on the order of the Planck temperature, independently of the mass and hence also of the Schwarzschild radius of a Schwarzschild black hole. We then explain the exponential nature of the gravitational frequency shift as a function of the gravitational potential. Next, we consider the firewall-mass problem, and provide an at least prima facie tentative resolution thereto based on: (i) the mass of a firewall being canceled by the negative gravitational mass = (negative gravitational energy)/c2 accompanying its formation, (ii) the unchanged observations of a distant observer upon formation of a firewall, and (iii) Birkhoff’s Theorem (actually first discovered by Jørg Tofte Jebsen). We then consider one aspect of thermodynamics in gravitational fields, showing that equilibrium relativistic gravitational temperature gradients cannot be exploited to violate the Second Law of Thermodynamics.

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Primordial Black Holes

Cited by 2 publications

References 85 publications

Testing the Minimum System Entropy and the Quantum of Entropy

Testing the Minimum System Entropy and the Quantum of Entropy

Firewalls, Hawking (Tolman) Radiation, and a Tentative Resolution of the Firewall-Mass Problem

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